The present invention relates to safety systems aboard an aircraft. In particular, the invention relates to an operation mechanism adapted for activating a deceleration device for decelerating an opening movement of a door in the event of a cockpit decompression. Moreover, the invention relates to a cockpit door arrangement comprising such an operation mechanism and to a use of such an operation mechanism aboard an aircraft.
The cockpit door aboard an aircraft provides the primary means of dissipating pressure from the cabin to the cockpit during a cockpit decompression case. A cockpit decompression case may occur as a minimal opening involving relatively slow bleed of pressure up to a maximum opening (as defined by aviation authorities) involving a rapid loss of pressure. To ensure that the delta pressure build up upon the monuments and structure that form the physical barrier between the cabin and cockpit does not exceed the structural limitations, the cockpit door must release and open to a specific venting area within a short time frame. Delay of the door to provide adequate venting may result in catastrophic structural failure.
The total time frame for the door to provide an effective venting area may be defined as the time [ms] for releasing the door lock and the time [ms] for rotating the door open, for example to an opening angle of more than 80°.
To satisfy certain certification requirements defined by aviation authorities, it has to be demonstrated that an aircraft can survive a decompression case without subsequent loss of essential structure/equipment and life. For example, JAR 25.365(e) (2) specifies that the aircraft structure must be able to withstand the depressurization caused by an instant opening of a predetermined area in the pressurized shell, at any operating altitude.
From the beginning of a cockpit decompression event to the point of door lock release delta air pressure is acting upon the door, as time from the decompression event increases, so the delta air pressure load upon the door increases. The delta air pressure load causes the door to rotate open and accelerate, imparting kinetic energy into the door. In this connection, the resultant kinetic energy is dependant upon the air pressure load over time and the moment of inertia (MOI) of the door. This means that the slower the door is unlocked the higher the delta air pressure load at the point of release and that the higher the MOI of the door the longer the duration of (high) air pressure upon the door. Both factors increase the final kinetic energy of the door. Thus cockpit doors that are compliant with the post 9/11 security rules have a high kinetic energy due to the reinforced construction of the door.
Therefore, the cockpit doors should unlock rapidly and rotate through to a minimum venting area (for example more than 80°) as quickly as possible in the event of a cockpit decompression.
Once the door has rotated open sufficient to provide effective venting it must be decelerated, wherefore the energy present in the door must be dissipated without the door detaching (from its hinges) and without damage to the airframe. In particular, since a seat may be installed in the path of the rotating door, it must be ensured that no injuries will be caused to a flight crew member on that seat. Otherwise, without an effective means of energy dissipation, the door, once it has passed 90 degrees, will collide with the seat causing potential injury to occupant and possible detachment of the seat and/or detach the door from its hinges, causing unacceptable structural/equipment damage and possible crew injury.
The energy present in the door must be absorbed without adversely affecting the cockpit wall pressure difference. Allowing the door to rotate open unhindered to the minimum free venting area would advantageously limit the pressure difference load upon the cockpit wall. However the distance to decelerate the door before impact with the adjacent seat is minimal and amounts to approximately 13° of rotation in A 380 aircraft only. In this case, the resultant equivalent static reaction load applied at the centre of area of the door would be in excess of 4500 daN (4.500 kg), whereby the door as well as the adjacent seat might be damaged.